Enable composefs by default

See: https://pagure.io/workstation-ostree-config/pull-request/591
     https://fedoraproject.org/wiki/Changes/ComposefsAtomicCoreOSIoT
     https://fedoraproject.org/wiki/Changes/ComposefsAtomicDesktops

Signed-off-by: Paul Whalen <pwhalen@fedoraproject.org>

composefs.yaml

@@ -0,0 +1,12 @@
+# Enable composefs
+# See: https://fedoraproject.org/wiki/Changes/ComposefsAtomicDesktops
+# https://fedoraproject.org/wiki/Changes/ComposefsAtomicCoreOSIoT
+postprocess:
+  - |
+    #!/usr/bin/env bash
+    set -xeuo pipefail
+
+    cat >> /usr/lib/ostree/prepare-root.conf << 'EOF'
+    [composefs]
+    enabled = yes
+    EOF

fedora-iot-base.yaml

@@ -2,6 +2,8 @@ include:
   - bootupd.yaml
   # Workaround for https://bugzilla.redhat.com/show_bug.cgi?id=2305291
   - grub2-workaround.yaml
+  # Enable composefs
+  - composefs.yaml
 ref: fedora/rawhide/${basearch}/iot
 repos: []
 selinux: true